1. Field of the Invention
The present invention relates to an arrangement for synchronizing one or more input/output devices in teleprinters, and more particularly to such synchronization in the context of the subdivision, necessitated by the use of a five-bit code (CCITT 2) for communications transmission purposes, of the total quantity of characters into letters/figures levels.
2. Description of the Prior Art
When using a five-bit code, as for example the CCITT number 5 code, in teleprinter operations, for reasons which are due to the restricted number of combinations available (32 possibilities) from 5 bits and due to the large quantity of characters (letters, figures, commands) required to be transmitted, on the other hand, it is necessary to divide this quantity into subsidiary quantities, so-called levels, and to characterize each of these by the use of a special switching symbol. In this context, the totality of letters involved is assigned the switching symbol Bu and the totality of figures involved is assigned the switching symbol Zi. Depending upon the design of the teleprinters being used, with each change in level (shift) a switching symbol must be introduced either manually or by means of an automatic system. This switching symbol or signal ensures that the levels are synchronized between the transmitting and receiving stations, or between the corresponding input and output devices within one teleprinter where, for example, the keyboard (input device) is being used to operate through a perforator (output device) in order to record a punched tape.
In modern teleprinters, an automatic device ensures that switching symbols for synchronizing the letters/figures levels of several communicating teleprinters are inserted. Generally speaking, by means of an additional device, when operation commences, and with any change in the mode of operation, the communicating teleprinters are first of all placed in a neutral condition and then, prior to the transmission of a level-related character, a switching symbol is introduced. When using punched tapes, these switching symbols may be perceptible, and this constitutes a drawback. If, for example, a punched tape which is to be corrected is stopped in the reader unit at the character requiring correction, and if this character is then corrected by means of the keyboard, then in the new punched tape, before the character which is to be corrected, a switching symbol is punched unnecessarily because a change in mode of operation has taken place at that point. This introduction of unnecessary switching symbols constitutes a particular disadvantage in that the same is a nuisance when the teleprinter is being employed in association with electronic data processing systems which involve the production of punched tapes of proper format throughout.